Irradiation of lithium base greases



Unite Si te Patented June 27, 1961 IRRADIATION F LITHIUM BASE GREASES Alvin M. Natkin, Metuchen, John J. Kolfenbach, Plainfield, and Eric 0. Forster, Scotch Plains, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Mar. 23, 1956, Ser. No. 573,323

. Claims. (Cl. 204-154) This invention relates to lubricating grease compositions, and more particularly to a process of improving the physical properties of lithium base lubricating greases. In brief compass, the invention pertains to subjecting lithium base lubricating greases to high intensity ionizing radiation to obtain greases having higher dropping points, color and odor improvement, etc.

In the prior art, improved physical properties of lubricating greases have usually been attained through the use of special refining or finishing methods, unique thickening agents or oil bases and particular additives. In accordance with the present invention, it has now been found that physical properties of certain lubricating greases can be markedly improved by irradiation of the greases with high intensity ionizing radiation comprising gamma rays. This process has the advantages that in many instances it is less expensive than the prior art methods, it is more easily controlled, and it is more readily adaptable to a continuous operation.

The gamma rays with which the lubricating greases of the invention are irradiated may be derived from the radioactive decay of certain natural or artificially radioactive elements or isotopes such as radium 226, radium A, radium B, radium 'C, radium D, thallium 210, cobalt 60, cesium 137, europium 152-154, cesium 134, cerium 144, silver 110, thulium 170, tantalum 182, scandium 46, terbium 160 or iridium 192 or from chemical compounds of or materials containing such elements or isotopes. The gamma rays may also be derived from suitably "shielded radiation produced in nuclear reactors, i.e.

atomic piles, or from the spent fuel elements obtained from the operation of such reactors.

In general, undisturbed gamma ray fluxes within the range of about to 6x10 usually about 10 to 3 X10 roentgens per hour, such as that derived from a cobalt 60 source, will be employed in irradiating the lithium base lubricating greases. The time of irradiation will depend upon the degree of change in the physical prop erties of the lubricating greases desired as well as upon the radiation dosage rate. The total radiation dosage (based on undisturbed radiation field conditions, i.e. con ditions prior to the introduction of the lubricating oil into the radiation field) will ordinarily be within the range of about 10 to 3x10 preferably about 10 to 3x10 roentgens of gamma rays. Thus, irradiation time may vary from about 0.01 to 3000 hours, usually about 0.5 to 200 hours. For the purposes of this invention, however, the lubricating grease need only be irradiated for a suflicient period of time to obtain the desired change in physical properties.

The lithium base greases may also be irradiated in an atomic pile wherein the radiation will consist primarily of fast and slow neutrons and gamma rays.

The lithium base lubricating greases employed in the invention may be any of the lithium soap thickened greases described in chapter 10 of Boners Manufacture and Application of Lubricating Greases (Reinhold Publishing Corp). The naturally occurring or synthetic fats or fatty acids employed in formulating the lithium greasethickening soaps may be any of the commonly known grease-making materials. Examples of these materials include saturated or unsaturated fatty acids having iodine numbers within the range of about 0 to 154 and having about 12 to 30, preferably about 18 to 22, carbon atoms per molecule, such as lauric, myristic, palmitic, stearic, 12-hydroxy stearic, 9,10-dihydroxy stearic, behenic, myristoleic, palmitoleic, oleic, linoleic lignoceric, ricinoleic and ,erucic acids, cottonseed oil fatty acids, animal fatty acids, palm oil fatty acids, hydrogenated fish oil fatty acids and their mixtures and/or their glycerides such as lard, beef, rapeseed, palm, menhaden, herring, castor oils, etc.

The lubricating oil menstruum may be any of the conventionally used mineral, animal, vegetable or synthetic lubricating oils. In general, these lubricating oils should have a viscosity of about 50 to 2,000 SUS at 100 F. and about 35 to 200 SUS at 210 R, an A.S.T.M. pour point of about +20 to F., a flash point of about 350 to 650 F. and a viscosity index of about 0 to 60 or higher. Conventionally refined and treated mineral oil base stocks which are derived from paraflinic, naphthenic and mixed base crudes and have the properties listed above are especially useful in preparing the lithium base lubricating grease compositions.

The synthetic lubricating oils Which may also be employed include esters of monobasic acids (e.g. an ester of C Oxo alcohol with C Oxo acid, an ester of C Oxo alcohol with octanoic acid, etc.), esters of dib-asic acids (e.g. di-Z-ethyl hexyl sebacate, di-nonyl adipate, etc.), esters of glycols (e.g. C Oxo acid diester of tetraethylene glycol, etc.), complex esters (e. g. the complex ester formed by reacting one mol of tetraethylene glycol with two moles of sebacic acid and two moles of Z-ethyl-hexanol or the complex ester formed by reacting one mol of tetraethylene glycol, one mol of adipic acid, one mol of C OX0 alcohol and one mol of C Oxo acid, etc.), esters of phosphoric acid (e.g. the ester formed by contacting three moles of the mono-methyl ether of ethylen glycol with one mol of phosphorous oxychloride, etc.), halocarbon oils (e.g. the polymer of chlorotn'fluoroethylene containing twelve recurring units of chlorotrifluoroethylene), carbonates (e.g. the carbonate formed by reacting C Oxo alcohol with ethyl carbonate to form a half ester and reacting this half ester with tetraethylene glycol), mercaptals (e.g. the mercaptal formed by reacting 2-ethyl hexyl mercaptan with formaldehyde), formals (e.g. the formal formed by reacting C Oxo alcohol with formaldehyde), polyglycol type synthetic oils (e.g. the compounds formed by condensing butyl alcohol with fourteen units of propylene oxide, etc.), or mixtures of the above in any proportions.

The preparation of these simple lithium soap thickened greases may be carried out by any of the conventional processes described in sections 10:20 to 10:26 of chapter 10 of Boner, supra, or in US. Patent Nos. 2,274,673, 2,397,956 and 2,450,221. Since the preparation of lubricating greases is not directly related to the present invention, these methods need not be described in detail.

In accordance With another aspect of this invention, mixed base lubricating greases containing soaps of two or more metals, at least one of the metals being lithium, may also be subjected to high intensity ionizing radiation. Such mixed base greases include, for example, lithium soap-alkaline earth metal soap greases. The alkaline earth metal may be calcium, barium, magnesium or strontium. Lubricating grease compositions containing lithium-calcium soap thickeners are the preferred mixed base greases of the invention. The composition and preparation of such greases are described in detail in US. Patent Nos. 2,641,577 and 2,646,401. In general, from about 2:1 to 8:1 mols of lithium soap to mols of calcium soap will be employed in preparing these greases. The saponifia-ble material and oil menstruum may be any of the materials listed above with respect to the preparation of simple lithium soap thickened greases.

4 Grease B:

Lithium stearate 21.73

In general, the lithium base greases will comprise (1) Zinc naphthenate 0.49 about 3 to 25 wt. percent, preferably about 6 to 20 wt. Ditertiary butyl para cresol 0.38 percent, of the thickening agent, i.e. the lithium soap or Corrosion inhibitor 1 1.25 the lithium soap-alkaline earth metal soap, and (2) about Di-Z-ethylhexyl sebacate 75.66 75 to 97 wt. percent, preferably about 80 to 94 wt. per- Phenyl'alpha naphthylamine 0.49 cent, of the lubricating oil. The greases may also con- Grease C: tain minor proportions of conventional grease additives. Lithium l2-hydroxy stearate 12.0 More particularly, they may contain oxidation inhibitors 10 Mineral lubricating oil, 55 SUS 210 F. 88.0 (e.g. phenyl alpha naphthylamine and ditertiary butyl Grease D: para cresol), corrosion inhibitors (e.g. zinc dialkyl dithio- Lithium stearate 12.0 phosphate), rust inhibitors, dyes, etc. Mineral lubricating oil, 55 SUS 210 F. 88.0

The irradiation of the lithium base greases may be carried out by a variety of procedures. For example, the Patent radioactive source may be placed in atank containing the The effect of gamma ray irradiation on the above 7 greases to carry out a batch operation or the radioactive greases is set forth in the following tables: 1

TABLE I Dropping Pt., F. Unworked Micro Neut. N0.

Penetration, mm./10 Greases Before After Percent Before After Percent Before After Change Change Change (NaOH) l Lighter in color following irradiation. 2 Percent oleic acid. 3 Lost characteristic ester smell following irradiation.

source may be placed into a stream of the grease for a TABLE H continuous or semi-continuous operation. Many obvious Norma-Hofimann bom'b oxidation test modifications of these procedures will be apparent to those skilled n the art. The utilization of radiation Time, in hours, for 0, pressure to drop emitted by radioactive material Will necessitate, of course, Greases v adequate radiation shielding means and techniques. 40 51bs 101m 201bs 301b,, Such means and techniques are, however, well known in t the art and need not be described here in detail. o{befm.em.adiafion 26 36 l The irradiation of the lithltun base greases may genafter irradiati0r1 5s 72 7s erally be carried out at temperatures within the range of n{gf g;g igg figgfi; g2 i3 32 g? about 20 to 400 F. or higher. In general, the irradiation will be carried out at a temperature of about 50 to 250 F., preferably about 75 to 150 F. and under vacuum or elevated pressures, such as about 2 to 50 atmospheres. However, one of the advantages of the present process is that it may be effectively utilized at room temperature and at atmospheric pressure.

The following example and tables are presented to illustrate the preparation and various characteristics of the improved lithium base greases of the invention:

EXAMPLE A number of lithium base lubricating greases were irradiated by filling one ounce screw-top bottles to the neck with the lubricating grease, closing the bottle with a plastic screw-top to leave very little air in the container, and then lowering the bottles into the center of a cylindrical cobalt source. The undisturbed radiation intensity of source used to irradiate greases A and B was about 2.2x l0 roentgens per hour, whereas an undisturbed radiation intensity of about 1.74 10 roentgens per hour was used in the case of greases C and D. All of the greases were irradiated for 168 hours at a temperature of about 100 F.

The greases had the following formulations:

Wt. percent Grease A:

Hydrated lime 0.85 Lithium hydroxy monohydrate 1.90

Cottonseed fatty acids 15.00 Mineral lubricating oil, 70 SUS 210 F. 82.25

45 The above data show that physical properties of lithium base lubricating greases can be markedly improved by subjecting the greases to high intensity ionizing radiation comprising gamma rays. It should be noted from Table I that each of the irradiated greases showed a significant increase in dropping point without deleterious effects with respect to other grease characteristics such as penetration, i.e. consistency, or neutralization number. In addition, grease A, a lithium-calcium base grease, became lighter in color after being subjected to irradiation, while grease B, a synthetic ester base grease lost its characteristic ester smell. As further shown in Table II, greases C and D were also significantly improved with respect to oxidation resistance.

It will be further understood that the invention is not necessarliy limited to the specific materials and operating conditions of the foregoing examples. These materials and conditions may be varied within the limits indicated in the general portions of the specification.

What is claimed is:

1. A method for increasing the dropping point of a lubricating grease comprising a lubricating oil and a thickening amount of a lithium soap, which comprises subjecting said grease to a radiation dosage sufficient to increase the dropping point of said grease and within the range of about 10 to 3X10 roentgens of gamma rays, and recovering a lubricating grease having a dropping point at least 10 F. higher than the nonirradiated grease.

2. The method according to claim 1 wherein said lubrieating oil is a mineral lubricating oil and said lithium soap is a soap of a carboxylic acid having from about 12 30 carbon atoms per molecule.

3. The method of claim 1 wherein said lubricating oil' References Cited in the file of this patent UNITED STATES PATENTS 2,637,695 McKinley et a1. May 5, 1953 6 2,719,122 Morway Sept. 27, 1955 2,743,223 McClinton Apr. 24, 1956 FOREIGN PATENTS 665,263 Great Britain Jan. 23, 1952 154,213 Great Britain Apr. 24, 1922 66,034 France Dec. 12, 1955 (4th addition to No. 1,079,401)

OTHER REFERENCES Mincher: KAPL731, pp. 3-8, Apr. 2, 1952. Declassified :Feb. 15, 1955.

Chem. and Eng. News, vol. 35, No. 17, page 28, Apr. 29, 1957.

Proceedings of the Second United Nations Interna tional Conference on the Peaceful Uses of Atomic Energy, vol. 29, pp. 276-286 (1958). 

1. A METHOD FOR INCREASING THE DROPPING POINT OF A LUBRICATING GREASE COMPRISING A LUBRICATING OIL AND A THICKENING AMOUNT OF A LITHIUM SOAP, WHICH COMPRISES SUBJECTING SAID GREASE TO A RADIATION DOSAGE SUFFICIENT TO INCREASE THE DROPPING POINT OF SAID GREASE AND WITHIN THE RANGE OF ABOUT 10**5 TO 3X10**10 ROENTGENS OF GAMMA RAYS, AND RECOVERING A LUBRICATING GREASE HAVING A DROPPING POINT AT LEAST 10*F. HIGHER THAN THE NONIRRADIATED GREASE. 